I. Field of the Invention
The present invention relates generally to ophthalmic instruments, and more particularly to subjective ophthalmic refractors for evaluating refractive characteristics of a patient""s eye.
II. Description of the Related Art
A subjective ophthalmic refractor typically comprises left-eye and right-eye batteries each having a defined viewing path along which an operator may selectively introduce combinations of testing lenses having known refractive properties. During examination, the patient is positioned in a darkened room with his or her eyes aligned to view a projected target chart along the viewing paths defined by the left-eye and right-eye batteries. The operator then performs well-known refracting procedures, including refraction using astigmatic charts and the Jackson cross-cylinder test. A goal of the examination procedure is to determine the sphere power, cylinder power, and cylinder axis of each eye in order to prescribe a suitable pair of corrective lenses.
In order to assess sphere power, the operator must rotate a strong sphere control knob and a weak sphere dial on the associated refractor battery to position chosen spherical power lenses in series in the viewing path. The numerical diopter value of the resultant sphere power introduced in the viewing path is reported to the operator by a sphere power readout provided on the refractor battery. A rotatable cylinder power control knob enables the operator to adjust the power of a cylinder lens introduced in the viewing path, and a numerical diopter value of the cylinder power is displayed by a cylinder power readout on the refractor battery. The axis orientation of the cylinder lens is controlled by a cylinder axis knob that includes a pair of diametrically opposite cylinder axis pointers. The cylinder axis knob is mounted for rotation relative to a coaxially arranged cylinder axis scale circumferentially surrounding the cylinder axis knob and having angular scale gradations. Typically, the scale gradations are marked in five-degree increments, and two complementary protractor scales of one-hundred eighty degrees surround the cylinder axis knob.
Because the examination room is darkened for purposes of target chart projection, the task of reading the sphere power and cylinder power readouts, and of finding the location of the cylinder axis pointers with respect to the cylinder axis scale, is a difficult one for the operator. During the course of a day in which the operator sees many patients, fatigue becomes a factor and the likelihood of errors in reading the refraction data increases. Operators have been known to use a pocket ophthalmoscope to illuminate the sphere and cylinder power readouts and the cylinder axis scale, however this is not the intended use of an ophthalmoscope.
The R. H. Burton Company of Grove City, Ohio has addressed this problem by providing an ophthalmic refractor wherein the sphere power readout, the cylinder power readout, and the cylinder axis scale are illuminated according to an arrangement described in U.S. Pat. No. 5,281,984. This patent teaches the use of a single light bulb supplying light to a light guide mounted on the refractor battery housing of each refractor battery. The light guide is formed of transparent material and is configured to provide a first transparent output around the periphery of the cylinder axis scale, a second transparent output adjacent to the cylinder power readout, and a third transparent output adjacent to the spherical power readout. While this arrangement solves the problem in a suitable manner, it does have certain drawbacks. For example, when the bulb burns out, illumination is ceased at the sphere power readout, the cylinder power readout, and the cylinder axis scale all at once. Another drawback is that the specially configured light guide is not retrofittable to older refractor models from R. H. Burton Company and to ophthalmic refractors from other manufacturers. Finally, the patent contains no teaching of how to arrange a power supply cord connected to the bulb in a manner that will not interfere with the patient or operator.
Therefore, it is an object of the present invention to provide an ophthalmic refractor with means for illuminating a sphere power readout, a cylinder power readout, and a cylinder axis scale of the refractor such that they may be readily and clearly viewed by an operator in a darkened examination room.
It is another object of the present invention to provide an ophthalmic refractor with means for independently illuminating a sphere power readout, a cylinder power readout, and a cylinder axis scale of the refractor such that an illumination source failure with respect to one of these elements does not affect illumination of the other elements.
It is a further object of the present invention to provide an ophthalmic refractor with means for connecting a power source to various illumination sources thereof such that power cords or the like are unobtrusive to the patient and operator.
It is a further object of the present invention to provide an ophthalmic refractor with means for illuminating a sphere power readout, a cylinder power readout, and a cylinder axis scale of the refractor that is retrofittable to a wide range of ophthalmic refractor models.
It is a further object of the present invention to provide a method of retrofitting an ophthalmic refractor with means for illuminating a sphere power readout, a cylinder power readout, and a cylinder axis scale of the refractor.
The present invention involves improvement of a subjective ophthalmic refractor of the type comprising left-eye and right-eye batteries, a mounting bracket for pivotally suspending the left-eye and right-eye batteries from a stand, each battery having a patient viewing path, a strong sphere control knob for selectively positioning a strong sphere lens of chosen power in the patient viewing path, a weak sphere control dial for selectively positioning a weak sphere lens of chosen power in the patient viewing path, a sphere power readout for displaying the cumulative power of the chosen strong and weak sphere lenses to an operator, a cylinder power knob for selectively positioning one or more cylinder lenses of chosen power in the patient viewing path, a cylinder power readout corresponding to the cylinder power knob for displaying the resultant power of the cylinder lenses to an operator, a polar cylinder axis scale, and a cylinder axis knob coaxial with and rotatable relative to the cylinder axis scale for adjusting the cylinder axis of the cylinder lenses, wherein the cylinder axis knob includes at least one cylinder axis pointer cooperating with the cylinder axis scale for indicating the cylinder axis to an operator. An ophthalmic refractor of the above-mentioned type is improved by forming the cylinder axis scale as a light-transmitting component having opaque scale gradations, and installing a polar array of illumination sources arranged to project light through the cylinder axis scale. The cylinder axis scale preferably includes a translucent material for diffuse illumination. In an alternative embodiment, the cylinder axis scale simply includes a photoluminescent material having scale gradations applied thereto. To enhance the visibility of the cylinder axis pointers with respect to the cylinder axis scale, the cylinder axis pointers are preferably formed as light-transmitting areas on the cylinder axis knob that overlap with the cylinder axis scale, or the pointers are opaque markings on an annular translucent flange overlapping with the cylinder axis scale.
The ophthalmic refractor is further improved by installing a cylinder power illumination source near the cylinder power readout, and by installing a sphere power illumination source near the sphere power readout.
In a preferred embodiment of the invention, the light sources are light-emitting diodes connected to a power source via a slip ring arranged to conduct electricity through the pivotal connection between the mounting bracket and the remainder of the refractor, whereby external power cords in the region of the patient or the operator can be avoided.
The invention further encompasses a method for retrofitting an ophthalmic refractor of the above-mentioned type. The method comprises the steps of removing the cylinder axis knob and cylinder axis scale from each battery housing, opening each battery housing, fixing a polar array of illumination sources within each battery housing, arranging power lines leading to each polar array of illumination sources for enabling a power source to be connected the arrays, closing each battery housing, and installing a replacement cylinder axis scale over each polar array of illumination sources, the replacement cylinder axis scale being formed as a light-transmitting component having opaque scale gradations, and mounting either the original cylinder axis knob or a replacement cylinder axis knob to be coaxial with the replacement cylinder axis scale. Where the original cylinder axis knob is reused, machining a cut-out area in place of a cylinder axis pointer on the cylinder axis knob is a preferred additional retrofit step. The method preferably comprises the further steps of installing a cylinder power illumination source in each battery housing proximate the respective cylinder power readout, and installing a sphere power illumination source in each battery housing proximate the respective sphere power readout.